April 06, 2009
Steve Cole
Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov
Jane Beitler
National Snow and Ice Data Center, Boulder, Colo.
303-492-1497
jbeitler@nsidc.org
RELEASE: 09-079
SATELLITES SHOW ARCTIC LITERALLY ON THIN ICE
WASHINGTON -- The latest Arctic sea ice data from NASA and the
National Snow and Ice Data Center show that the decade-long trend of
shrinking sea ice cover is continuing. New evidence from satellite
observations also shows that the ice cap is thinning as well.
Arctic sea ice works like an air conditioner for the global climate
system. Ice naturally cools air and water masses, plays a key role in
ocean circulation, and reflects solar radiation back into space. In
recent years, Arctic sea ice has been declining at a surprising rate.
Scientists who track Arctic sea ice cover from space announced today
that this winter had the fifth lowest maximum ice extent on record.
The six lowest maximum events since satellite monitoring began in
1979 have all occurred in the past six years (2004-2009).
Until recently, the majority of Arctic sea ice survived at least one
summer and often several. But things have changed dramatically,
according to a team of University of Colorado, Boulder, scientists
led by Charles Fowler. Thin seasonal ice -- ice that melts and
re-freezes every year -- makes up about 70 percent of the Arctic sea
ice in wintertime, up from 40 to 50 percent in the 1980s and 1990s.
Thicker ice, which survives two or more years, now comprises just 10
percent of wintertime ice cover, down from 30 to 40 percent.
According to researchers from the National Snow and Ice Data Center in
Boulder, Colo., the maximum sea ice extent for 2008-09, reached on
Feb. 28, was 5.85 million square miles. That is 278,000 square miles
less than the average extent for 1979 to 2000.
"Ice extent is an important measure of the health of the Arctic, but
it only gives us a two-dimensional view of the ice cover," said
Walter Meier, research scientist at the center and the University of
Colorado, Boulder. "Thickness is important, especially in the winter,
because it is the best overall indicator of the health of the ice
cover. As the ice cover in the Arctic grows thinner, it grows more
vulnerable to melting in the summer."
The Arctic ice cap grows each winter as the sun sets for several
months and intense cold sets in. Some of that ice is naturally pushed
out of the Arctic by winds, while much of it melts in place during
summer. The thicker, older ice that survives one or more summers is
more likely to persist through the next summer.
Sea ice thickness has been hard to measure directly, so scientists
have typically used estimates of ice age to approximate its
thickness. But last year a team of researchers led by Ron Kwok of
NASA's Jet Propulsion Laboratory in Pasadena, Calif., produced the
first map of sea ice thickness over the entire Arctic basin.
Using two years of data from NASA's Ice, Cloud, and land Elevation
Satellite (ICESat), Kwok's team estimated thickness and volume of the
Arctic Ocean ice cover for 2005 and 2006. They found that the average
winter volume of Arctic sea ice contained enough water to fill Lake
Michigan and Lake Superior combined.
The older, thicker sea ice is declining and is being replaced with
newer, thinner ice that is more vulnerable to summer melt, according
to Kwok. His team found that seasonal sea ice averages about 6 feet
in thickness, while ice that had lasted through more than one summer
averages about 9 feet, though it can grow much thicker in some
locations near the coast.
Kwok is currently working to extend the ICESat estimate further, from
2003 to 2008, to see how the recent decline in the area covered by
sea ice is mirrored in changes in its volume.
"With these new data on both the area and thickness of Arctic sea ice,
we will be able to better understand the sensitivity and
vulnerability of the ice cover to changes in climate," Kwok said.
For more information about Arctic sea ice, visit:
http://www.nasa.gov/topics/earth/features/arctic_thinice.html
and
http://nsidc.org/arcticseaicenews
For more information about NASA and agency programs, visit:
http://www.nasa.gov
-end-